1. Field of the Invention
The present invention relates to an electrode comprising a current collector and an active material layer, and a battery using it.
2. Description of the Related Art
In recent years, mobile devices have become sophisticated and multifunctional. Along with these situations, a high capacity secondary battery has been desired as a power source for these mobile devices. As a secondary battery corresponding to such a desire, there is a lithium ion secondary battery. However, in the case using a typical lithium secondary battery, wherein cobalt acid lithium is used for a cathode and graphite is used for an anode, the battery capacity is in a saturation state, and a significantly high capacity is hard to be realized. Therefore, from long time ago, it has been considered to use metal lithium (Li) for the anode. However, in order to put this anode into practical use, it is necessary to improve precipitation-dissolution efficiency of lithium, and control dendrite precipitation feature.
Meanwhile, recently, a high capacity anode, wherein silicon (Si), germanium (Ge), tin (Sn) or the like is used is actively considered. However, when charge and discharge is repeated, this anode is crushed to fine particles due to intense expansion and shrinkage of the anode active material. In result, its current collecting characteristics deteriorate, decomposition reaction of the electrolytic solution is promoted due to increase in the surface area, and its cycle characteristics are very poor. Therefore, an anode, wherein an active material layer is formed on an current collector by vapor-phase deposition method, liquid-phase deposition method, sintering method or the like has been considered (for example, refer to Japanese Unexamined Patent Application Publication No. H8-50922, Japanese Patent No. 2948205, and Japanese Unexamined Patent Application Publication No. H11-135115). According to this anode, compared to the conventional coating-type anode, wherein a slurry containing a particle active material and a binder is coated, to become fine particles can be inhibited, and the current collector and the active material layer can be integrated. Therefore, electronic conductivity in the anode becomes very excellent, and it is expected that its capacity and its cycle life would be sophisticated. Further, in this case, it is possible to reduce or exclude a conductive material, a binder, voids or the like, which have been existed in the conventional anode. Consequently, the anode can become a thin film essentially.
However, also in this anode, the active material falls off due to expansion and shrinkage of the active material according to charge and discharge, and its cycle characteristics are not sufficient. Further, reactivity with the electrolyte is still high. Therefore, lowering of the battery capacity is induced by reaction with the electrolyte according to charge and discharge.